Why did King James Executed Sir Walter Raleigh?

King James I executed Sir Walter Raleigh in 1618 primarily due to Raleigh's involvement in a failed expedition to South America, which was seen as treasonous. Raleigh had previously been imprisoned for many years for his political machinations and had been released on the condition that he would not engage in further exploration. His return to warlike activities and the subsequent discovery of a plot against the king led to his trial and execution, as James sought to assert his authority and discourage rebellion.